The present invention relates to an inclination angle sensor to be mounted on a vehicle such as an automobile for measuring an inclination angle of the vehicle with respect to a direction of gravity.
As one of safety mechanisms for automobiles, airbag system that operates in the event of accident such as a head-on collision, a broadside collision, and the like, has spread widely in recent years. Since such accident may involve a turning-over of automobile, an inclination angle sensor capable of operating a safety mechanism by detecting behavior of a rotating vehicle is considered useful.
An inclination angle sensor disclosed in Japanese Patent Laid-Open Publication No. S60-154108 has been known in the past. FIG. 27 shows an inclination angle sensor of the prior art. A pendulum element 201 of flat plate changes its angle with respect to a base plate 202 according to an inclination angle of an automobile. The angle is detected with presence or absence of transmitted light of a transmission type photo-interrupter 204 mounted by an outer periphery of the pendulum element 201 in a manner to sandwich slits provided along the outer periphery of the pendulum element 201. Magnets 203 are also provided on the base plate 202, so that the pendulum element 201 rotates in a direction traverse to a magnetic flux of the magnet 203. When the pendulum element 201 rotates at a speed of xe2x80x9cVxe2x80x9d, an induction voltage is generated within the pendulum element 201 in a direction perpendicular to the rotational direction, and an eddy current is generated by the induction voltage. The eddy current then generates a force in proportion to the speed xe2x80x9cVxe2x80x9d within the pendulum element 201 in a direction opposite to the rotational direction, and this force functions as a damping force to stabilize rotation of the pendulum element 201.
Inclination angle sensors of this kind for installation in vehicles such as automobiles are required to be small in size and superior in rotational performance, since they are mounted within a control unit.
However, the foregoing inclination angle sensor of the prior art has a problem that it is difficult to reduce the size because of structural restrictions such as a diametrical dimension of rotary shaft and a center of gravity of the pendulum element, both of which affect the rotational performance, and the photo-interrupter, which needs to be mounted around an outer periphery of the pendulum element.
The present invention is intended to solve the foregoing problem, and it aims at providing an inclination angle sensor that can be mounted on a vehicle such as an automobile, small in size, and superior in rotational performance.
In order to solve the problem, an inclination angle sensor of the present invention includes: a weight of conductive and non-magnetic material; a rotary shaft fixed to the weight; a bearing for rotatably supporting the rotary shaft; a frame for securing the bearing; one or two combinations of reflection type photo-interrupter consisting of a light-emitting element and a light-receiving element of which signal vary in response to a movement of the weight; a flange part provided to outstretch from an outer perimeter of the weight in parallel to or in a manner to form a predetermined angle with the rotary shaft; a magnet fixed to the frame in a manner produce magnetic flux primarily toward the flange part; and a circuit unit for processing the signal.
The foregoing structure realizes the inclination angle sensor that is small in size and superior in rotational performance.